1. Field of the Invention
The present invention relates to the mounting of telescopic sights on guns, especially on semiautomatic shotguns. It is necessary for the telescopic sight to be rigidly mounted to the gun so that the line of sight is precisely parallel to the bore of the gun. Moreover, the sight's rigid mounting must withstand repeated heavy shocks from the recoil of the gun as it is fired. That is, the sight must be mounted so rigidly to the gun that the repeated heavy shocks do not generally affect the precise parallelism of the sight's tube and the gun's bore. Though occasional adjustment may be necessary, this parallelism must be maintained insofar as possible.
2. Prior Art
Most guns, especially semiautomatic shotguns, have a receiver made from metal that is substantially thinner at the top than at the sides. The top of the receiver is thus too thin to permit tapping and drilling for screws strong enough to hold the mounting for a conventional telescopic sight. On certain guns, e.g., Browning Model A-5, Remington Model 1100, and Remington Model 11-87, the receiver is so thin at the top that only two to two-and-a-half threads may be drilled therein. So few threads are insufficient to hold the mount for a telescopic sight to the gun with sufficient rigidity to withstand normal use. A sight mounted with screws held by only two to two-and-a-half threads will quickly work loose in response to the gun's recoil when it is fired. A loose sight or one that is not rigidly mounted will cause shots from that gun to be inaccurate. Indeed, when a telescopic sight is attached to the thin top of a conventional receiver on a semiautomatic shotgun, the recoil from a single shot can detach the sight, thereby endangering the shooter. Such an accident is likeliest when the gun's receiver is made of aluminum, which is a relatively soft metal.
Hence it is conventional for gunsmiths to mount a telescopic sight on such a gun by means of a side mount, such as a Weaver mount. Such a side mount is used because the side of the receiver on such a gun is sufficiently thick to hold the mount rigidly, having a thickness that supports approximately five threads. Unfortunately, however, mounting the sight on one side of the gun creates unnecessary bulk, in that a side mount projects from the gun at an angle of approximately 45 degrees from the vertical to clear the gun's receiver and then reverses to place the sight into vertical alignment with the gun's bore. A side-mounted sight is also difficult to align with the bore. Thus mounting a sight from one side only in the customary way can reduce both the comfort of the weapon and the accuracy of fire. Moreover, because a side mount is installed on one side of the receiver only, the sight it holds may work loose from the gun.